Problem 53 - Chemistry The Molecular Nature of Matter

Question

The iron(III) ion forms a complex with six cyanide ions that is often called the ferricyanide ion. What is the net charge on this complex ion, and what is its formula? What is the IUPAC name for the complex?

Step-by-Step Solution

Answer

The net charge on the ferricyanide ion is -3, and its formula is [Fe(CN)_6]^{3-}. The IUPAC name for the complex is hexacyanoferrate(III) ion.

Step 1: Determine the charge of the iron(III) ion

The iron(III) ion has a charge of +3, as indicated by the Roman numeral III in its name. Its symbol is Fe and the charge is written as Fe^{3+}.

Step 2: Determine the charge of the cyanide ion

The cyanide ion has a charge of -1 and is represented as CN^{-}.

Step 3: Calculate the total negative charge from cyanide ions

Since there are six cyanide ions, the total negative charge is 6 times -1, which totals -6.

Step 4: Determine the net charge of the ferricyanide ion

To balance the +3 charge of the iron(III) ion with the -6 total charge from the cyanide ions, the net charge of the complex is -6 + 3, which equals -3.

Step 5: Write the formula of the ferricyanide ion

Since we have one iron(III) ion and six cyanide ions, the formula of the ferricyanide ion is [Fe(CN)_6]^{3-}.

Step 6: Name the complex ion according to IUPAC nomenclature

According to IUPAC nomenclature, the name of the complex is hexacyanoferrate(III) ion.

Key Concepts

Complex Ions

Complex ions are a staple in the realm of chemistry, intriguing both for their structures and the roles they play in our world. They consist of a central metal ion surrounded by molecules or ions known as ligands. These ligands can be neutral or may bear a charge, and they attach to the metal ion through coordinate covalent bonds, creating a unique entity in terms of charge and reactivity.

Take for instance the vivid world of the ferricyanide ion, which brings together an iron ion with cyanide ligands. This complex specifically showcases a metal in its +3 oxidation state (iron(III)) encircled by six cyanide, or CN^-, ions. Each CN^- ligand donates a pair of electrons to the iron, stabilizing the complex through their sphere of negative charges. The net charge of a complex ion, crucial for understanding reactions and the composition of molecules, is the algebraic sum of the charge of the central metal ion and its surrounding ligands.

Ionic Charges

The concept of ionic charges is vital for delving into the world of ions, including complex ions. An ion's charge signifies whether it has gained or lost electrons, rendering it negatively or positively charged, respectively. For a neutral compound, the total positive and negative charges must balance to zero. This concept is exemplified when we consider that the ferricyanide ion's overall charge is -3.

When we analyze the ferricyanide ion further, we encounter an intriguing question: how do the charges on the individual ions combine to form the final charge of the complex? The iron(III) ion, denoted by Fe³⁺, carries a positive charge of +3. The cyanide ions, each with a charge of -1, collectively contribute -6. Together, they yield a net charge of -3 for the ferricyanide ion. Understanding these charges and how they combine is crucial because it affects the complex's ability to interact with other ions and molecules, influencing solubility, reaction pathways, and more.

IUPAC Nomenclature

Navigating the landscape of chemical names is made more precise through the International Union of Pure and Applied Chemistry (IUPAC) nomenclature, a standardized method for naming chemical compounds. The name provides a wealth of information about the composition and structure of the compound. In naming the complex ions, IUPAC guidelines dictate that we first state the number of each type of ligand in the complex, using Greek prefixes like 'hexa-' for six. Next, we specify the ligand's name, followed by the central metal's name along with its oxidation state in Roman numerals.

According to these rules, the ferricyanide ion's name unfolds as 'hexacyanoferrate(III)'. 'Hexa-' reflects the six cyanide ions, 'cyanoferrate' combines the ligand (with 'cyano-' indicating cyanide) and the iron metal, and '(III)' clarifies the iron's oxidation state. This systematic approach allows chemists to decode complex structures and engage effectively with the world of inorganic chemistry, providing a universal language for their discoveries and studies.